1. Technical Field
The present invention relates to an image display device, an image display system, and a method of controlling an image display device.
2. Related Art
In the past, there has been known a projector making the image projection possible only in a use-permission period set in advance (Japanese Patent Publication No. 2011-100376 (Document 1)). According to such a projector, the projector can be prevented from being used by another user if the projector is lent, and remains unreturned even after the end of the use-permission period.
Further, there has been known a projection display device, which superimposes a secondary image on a primary image when a predetermined time set in advance is reached. According to such a projection display device, it is possible to inform the user of the rental term in the case in which, for example, the projection display device (a projector) is lent (Japanese Patent Publication No. 2004-297557 (Document 2)).
As described in Document 1 and Document 2, the image display device such as a projector is often used for a rental purpose. In such a configuration, the rental company sets the rental term to the image display device when lending the image display device. Therefor, if extension of the rental term is desired, it is required that the image display device is returned once to the rental company to perform resetting of the rental term, or that the person in charge in the rental company visits the installation place of the image display device to perform resetting of the rental term. Therefore, there has been demanded the image display device the rental term of which can easily be changed.